The present invention relates to systems for controlling the operation of turbocharged internal combustion engines, and more specifically to systems for eliminating, or at least minimizing, transient turbocharger compressor surge.
Turbochargers are well known devices for pressurizing intake air entering the combustion chambers of an internal combustion engine and thereby increasing the efficiency and power output of the engine. In general, pressurizing the intake air increases the quantity of air entering the engine cylinders during the intake stroke, and this allows more fuel to be utilized in establishing a desired air/fuel ratio. Increased available engine output torque and power is thereby realized.
As is known in the art, turbochargers utilize outgoing exhaust gas from the engine to pressurize the intake air. Referring to FIG. 1, an example of a known internal combustion engine turbocharging system 10 is shown. Exhaust gases from the engine enter an exhaust gas inlet of turbocharger 12 via exhaust manifold 14 and strike a turbine wheel 16 causing it to rotate. Exhaust gases exit the turbocharger 12 via exhaust gas outlet 18. The rotational forces imparted to the turbine wheel 16 by the exhaust gases are transferred to a compressor wheel 22 of turbocharger 12 via shaft 20. As the piston 30 moves downwardly within cylinder 36 on the intake stroke, air is drawn from air inlet 24 into the combustion chamber 28, defined as the area above the piston 30, via intake manifold 26. The pressure provided by turbocharger compressor 22 increases the air pressure within intake manifold 26, thereby supplying additional air to the combustion chamber 28 and providing for injection of additional fuel quantities.
The compressed air in intake manifold 26 is mixed with fuel supplied by a fuel source (not shown), and this mixture is supplied to the combustion chamber 28 of an engine cylinder 36 via intake valve 32. The air/fuel mixture is then compressed and ignited during a known combustion process. As the piston 30 moves up during the exhaust stroke, burnt exhaust gases created by the combustion event are expelled from the combustion chamber 28 into the exhaust manifold 14 via exhaust valve 34.
Two types of compressor surge are known to occur in highly turbocharged engines. Perhaps the most common type, referred to here as steady state compressor surge, occurs under essentially steady state values of engine speed and engine fueling rates. As engine speed is decreased at high values of turbocharger compressor ratio, a turbocharger compressor surge threshold is eventually reached, and at engine speeds beyond this threshold, stable compressor flow is no longer possible. As a consequence, a sudden reversal in compressor and intake manifold air flow occurs, resulting in a surge conditions that causes intake manifold pressure to decrease by an amount generally proportional to the intensity of the surge condition.
A second and less common type of compressor surge, referred to here as transient compressor surge, does not require initial operation of the turbocharger compressor near the compressor surge threshold. Rather, transient compressor surge may initiate from normal compressor ratio/engine speed conditions. In contrast to steady state compressor surge, transient compressor surge is triggered by a sudden and substantial reduction in engine fueling rate. When engine output power is severely and rapidly dropped from an initially high value, the volume and flow of exhaust gas striking the turbine 16 is likewise rapidly reduced, thereby resulting in an instantaneous and severe drop in turbocharger driving force. Unfortunately, the air pressure within the intake manifold 26, which is typically at an initially high value due to the high engine power demand, decays much more slowly than the rate of reduction in turbocharger driving force. The air pressure within the intake manifold 26 under such conditions thus slows the rotational movement of the compressor wheel 26. Transient compressor surge occurs when the accumulated pressure in the intake manifold 26 exceeds the compressor""s ability to sustain positive air movement. Since the rate of intake manifold pressure decay is inversely proportional to the total mass of air in the intake system, factors and conditions such as large intake manifold volumes, high intake manifold pressure and low intake manifold temperatures tend to contribute to transient compressor surge.
The slow decay of intake manifold pressure during conditions of low engine power demand immediately following high engine output power operation can result in undesirable turbocharger surge conditions as just described. Turbocharger surge can damage the compressor and/or create excessive engine noise, sudden power loss and severe vibration, thereby adversely affecting engine performance and creating a potential for engine damage. As the engine operator attempts to bring the turbocharger out of surge by increasing engine speed, the surge condition of the compressor impedes the rotational movement of the turbine, thereby impeding or slowing the acceleration rate. Multiple occurrences of compressor surge may decrease the longevity of the turbocharger and engine.
Previous attempts at eliminating or minimizing transient compressor surge have led to undesirable side effects. For example, modifications to engine fuel system control algorithms and/or mechanical fuel systems have been devised to reduce the rate of response of the fuel system to changes in throttle position. However, the extent of response dampening required to eliminate transient surge produces an unacceptable loss in engine acceleration rate when demanded by the operator. Other attempts to eliminate or minimize compressor surge include systems that control the rate of change of delivered fuel upon detection of compressor surge. These systems are undesirable since they operate only after compressor surge is experienced.
What is therefore needed is a system for eliminating or minimizing transient compressor surge without negatively affecting engine acceleration or fuel economy of the engine to which the turbocharger is coupled, and which is operable to control turbocharger operation to avoid transient compressor surge conditions before such surge conditions occur.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a system for controlling transient compressor surge in a turbocharged internal combustion engine comprises a turbocharger including a turbocharger compressor fluidly coupled to a cylinder of an internal combustion engine via an intake manifold, means for determining an operating condition of the intake manifold and producing an intake manifold parameter signal corresponding thereto, a fuel system responsive to a fueling command to supply fuel to the engine, and a control circuit limiting the fueling command to a minimum fueling limit based at least on the intake manifold parameter signal to avoid turbocharger transient compressor surge.
In accordance with another aspect of the present invention, a method of controlling transient compressor surge in a turbocharged internal combustion engine comprises the steps of sensing at least one operating parameter of a turbocharged internal combustion engine, determining a minimum fueling value as a function of the at least one operating parameter, wherein the minimum fueling value corresponds to a minimum fueling condition at which turbocharger transient compressor surge is avoided, and fueling the engine with a lower fueling limit defined by the minimum fueling value.
One object of the present invention is to provide a system for controlling fueling of an internal combustion engine in a manner that avoids turbocharger transient compressor surge.
Another object of the present invention is to provide such a system by controlling fueling to establish a minimum fueling value as a function of at least one engine operating parameter.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.